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Calculation of the Liquidator’s performance

Although many Liquidator users, including myself, are convinced that the LQ does its job, unfortunately a few users reported here that their pool’s FC isn’t maintained properly by the LQ. I asked myself, based on my own system, what’s the LQ’s highest theoretical performance, namely how much FC it can deliver. As far as my pool is concerned it does its job. My pool needs about a 2.5 ppm FC feed per day, and the LQ delivered 3 ppm during 9 hours of night metering, while the flow meter was set at about 3.5. However, for some people this may not be enough, so I wondered what is the top theoretical performance.

The level of FC in the water layer above the bleach level varies as a function of the distance from the border between the two phases. I took a sample of the water near the outlet float. I diluted a 10 ml sample into 6 fl oz with distilled water and measured FC. The simple analysis showed that the level of FC that leaves the LQ and enters the pump is 231 ppm, assuming that all the FC that leaves the LQ enters the pump. This may not be true with the tubing that comes in the LQ box, but it’s fair to say that the loss is no greater than 10%. This is an undoubtedly a killer dosage. No wonder that cheap plastic tubing degrades, as reported here.

The following calculation is based on a 20k gal pool, a 50gpm flow rate and a 11/2” line. Those among you who are familiar with hydraulics are invited to confirm or dispute this calculation. Since the intake of the highly chlorinated water is done through a ¼” tubing, as compared to 1 ½” of the main pipes, I assumed that the maximum flow of the LQ intake is proportional to the square ratio of the pipes diameter. (1.5”/0.25”)**2 = 36. This means that when the LQ operates at its maximum theoretical flow, the chlorinated solution of 231 is diluted by a factor of 36, and thus, the maximum FC of the water feeding the pool is 6.4 ppm.

Assuming now that the pump works 12 hours, and the LQ operates at full theoretical flow, a 20k gal pool can be enriched by up to 11.5 ppm FC, based on 50 gpm total flow. This is impressive performance. If the bleach percentage is 12 instead of 6, the enrichment can reach 23 ppm FC.

Suppose the maximum flow of the LQ is not 50gpm/36 for any reason of unaccounted for head, but it's half of the calculated value. We still have an upper limit of 5.75 ppm FC enrichment for 12 hours with 6% bleach solution in the LQ. Still, it's a very good performance.

Therefore, if some people report their LQ not doing its job, it’s most likely because of low flow. Fix the flow and it’ll work. Also, make sure that your bleach doesn’t deteriorate for any reason. Test the FC level of the water at the top by proper dilution and you’ll have an idea how strong is your bleach. If you want to test you need to wait at least 24 hours after pouring in the bleach in order for the diffusing bleach to reach a steady state distribution in the water level above. Also, the level of FC in the top level will change when the amount of bleach at the bottom changes because the distance of the border from the top changes. Do all measurements when the border is approximately the same height.

Re: Calculation of the Liquidator’s performance

Depending on various plumbing details, the maximum flow rate through the Liquidator can be far lower than what you are seeing. What we really need is a way to figure out which pools are likely to have problems before installing a Liquidator.